Aluminum nitride ceramics, members for use in a system for producing semiconductors, corrosion resistant members and conductive members

ABSTRACT

An object of the present invention is to preserve the characteristic properties of an aluminum nitride ceramics and reduce its volume resistivity. An aluminum nitride ceramics contains boron atoms in an amount of not lower than 1.0 weight percent and carbon atoms in an amount of not lower than 0.3 weight percent and has a volume resistivity at room temperature of not higher than 1×10 12  Ω·cm. Alternatively, an aluminum ceramics comprises aluminum nitride and intergranular phases mainly consisting of boron nitride constituting a conducting path and has a volume resistivity at room temperature of 1×10 12  Ω·cm. Such ceramics may be obtained by holding a mixture at least containing aluminum nitride and boron carbide at a holding temperature not lower than 1400° C. and not higher than 1800 ° C. and then sintered at a maximum temperature higher than the holding temperature.

[0001] This application claims the benefits of Japanese PatentApplications P2001-358, 719 filed on Nov. 26, 2001 and P2002-307, 811filed on Oct. 23, 2002, the entireties of which are incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an aluminum nitride ceramicshaving a low volume resistivity, a member for use in a system forproducing semiconductors, a corrosion resistant member and a conductivemember.

[0004] 2. Related Art Statement

[0005] An aluminum nitride sintered body has excellent corrosionresistant property against various corrosive substances such as ahalogen-based gas and has thus been utilized for various members in asystem for producing semiconductors including a ceramic heater andelectrostatic chuck. A conventional dense aluminum nitride sintered bodyhas a volume resistivity higher than 10¹³ Ω·cm at room temperature. Itis therefore needed to reduce the volume resistivity of an aluminumnitride sintered body depending on intended applications. The applicantfiled the following aluminum nitride sintered bodies each having avolume resistivity at room temperature as low as about 10¹⁰ Ω·cm.

[0006] (1) A sintered body with a small amount of Y₂O₃ added (Japanesepatent publication 9-315, 867A)

[0007] (2) A sintered body with a small amount of CeO₂ added (Japanesepatent publication 2001-163, 672A)

[0008] The above aluminum nitride sintered bodies have a high purity ofaluminum nitride and a low volume resistivity at the same time, and thusmay be utilized for various applications including a base material foran electrostatic chuck.

[0009] On the other hand, it has been known to reduce the resistivity ofan aluminum nitride sintered body by adding a large amount (for examplenot lower than 30 volume percent) of a conductive ceramic material suchas silicon carbide and titanium nitride to provide a composite ceramics.

[0010] Further in some applications such as a base material for anelectrostatic chuck, the base material is used in a wider temperaturerange. It is thus demanded to provide a material having a reduceddependency of volume resistivity on temperature change. The applicantfiled US-2002-0110709-A1 and disclosed an aluminum nitride sintered bodyhaving a volume resistivity at room temperature of 10⁸ to 10¹² Ω·cm anda change of volume resistivity between 25 to 400° C. of the order ofabout 10³. The sintered body may be produced by adding samarium oxideinto powdery raw material of aluminum nitride. Japanese patentpublications 8-314953A and 8-350075A disclose a method for furtherreducing the dependency of volume resistivity on temperature of analuminum nitride sintered body. In the disclosure, a conductive ceramicshaving a metallic conductivity such as TiN is added into powdery rawmaterial of aluminum nitride in an amount of 10 to 30 weight percent.

SUMMARY OF THE INVENTION

[0011] In methods described in Japanese patent publication 9-315867A and2001-163, 672A, it is possible to reduce the volume resistivity ofaluminum nitride ceramics at room temperature to a value as low as 10 to10⁹ Ω·cm by adjusting a composition of starting material and sinteringconditions. The requirements for the composition and sinteringconditions are, however, strictly limited to reduce the volumeresistivity at a value not higher than 10¹⁰ Ω·cm.

[0012] In Japanese patent publications 8-314953A and 8-350075A,conductive ceramics is added into raw material of an aluminum nitride toprovide a composite ceramics. According to this method, it is necessaryto add a large amount of conductive ceramics into aluminum nitride rawmaterial to obtain a composite ceramics for sufficiently reducing thevolume resistivity of the sintered body. Characteristic properties ofaluminum nitride are, however, lost by adding a large amount ofconductive ceramics. For example, a high thermal conductivity, lowthermal expansion, corrosion resistant property and chemical stabilityof aluminum nitride are lost or reduced. It is therefore desired topreserve the characteristic properties of aluminum nitride and reduceits volume resistivity.

[0013] An object of the present invention is to preserve thecharacteristic properties of aluminum nitride and reduce its volumeresistivity.

[0014] Another object of the present invention is to provide a ceramicconductive member having corrosion resistant property by preserving thecharacteristic properties of aluminum nitride and reducing its volumeresistivity.

[0015] Another object of the present invention is to provide an aluminumnitride ceramics having a low volume resistivity at room temperature anda reduced temperature dependency of volume resistivity over a widetemperature range.

[0016] The present invention provides an aluminum nitride ceramicscontaining boron atoms in an amount of not lower than 1.0 weight percentand carbon atoms in an amount of not lower than 0.3 weight percent andhaving a volume resistivity at room temperature of not higher than1×10¹² Ω·cm.

[0017] The present invention further provides an aluminum nitrideceramics comprising aluminum nitride phase and intergranular phasesmainly consisting of boron nitride constituting a conductive path andhaving a volume resistivity at room temperature of not higher than1×10¹² Ω·cm.

[0018] The present invention further provides an aluminum nitrideceramics comprising aluminum nitride phase and intergranular phasesmainly consisting of boron nitride and having a volume resistivity atroom temperature of not higher than 1×10¹² Ω·cm, wherein 004 diffractionpeak of the intergranular phase has a spacing d004 of not lower than1.6650 angstrom.

[0019] The present invention further provides an aluminum nitrideceramics being produced by sintering a mixture at least containingaluminum nitride and boron carbide and having a volume resistivity atroom temperature of not higher than 1×10¹² Ω·cm.

[0020] The present invention further provides a member for use in asystem for producing semiconductors comprising the aluminum nitrideceramics.

[0021] The present invention further provides a corrosion resistant orconductive member comprising the aluminum nitride ceramics.

[0022] The present invention further provides a conductive member havinga volume resistivity at room temperature of not higher than 1×10⁶ Ω·cmand composed of an aluminum nitride ceramics containing aluminum nitridein a content of not lower than 80 weight percent.

[0023] The inventors have tried to add various additives into analuminum nitride ceramics, and studied the effects of the additives onthe volume resistivity of the resulting aluminum nitride ceramics. Theinventors have found that the volume resistivity at room temperature ofan aluminum nitride sintered body may be reduced to a value not higherthan 10¹² Ω·cm by adding a predetermined amount of boron carbide intoraw material of aluminum nitride and sintering the mixture underspecified conditions. The present invention is based on the discovery.

[0024] The volume resistivity may be reduced to a value not higher than10¹⁰ Ω·cm and further not higher than 10⁷ Ω·cm, by further increasingthe added amount of boron carbide, and/or, by holding at a temperaturebetween 1400 and 1800° C. before sintering at a maximum temperature. Theinventors have reached the surprising discovery that the volumeresistivity of an aluminum nitride ceramics may be still further reducedto a value not higher than 10⁶ Ω·cm and even not higher than 10² Ω·cm.An aluminum nitride ceramics having this level of volume resistivitybelongs to a conductive material and not to a semiconductor.

[0025] The inventors have further investigated the requirements ofaluminum nitride ceramics for enabling such reduction of the volumeresistivity. As described in the section of “examples”, intergranularphases mainly consisting of boron nitride are formed between aluminumnitride grains in a ceramics having a low resistivity. The intergranularphase usually has a plate-like shape as shown in FIG. 1. In an aluminumnitride ceramics with a reduced volume resistivity, such plate-likeintergranular phases are sufficiently grown to form a kind of continuousphase or network microstructure. As described later, the inventors haveobserved the current distribution of an aluminum nitride sample andfound that the plate-like intergranular phases function as a conductivepath, for example as shown in FIG. 4. It has been thus proved that theintergranular phases mainly consisting of boron nitride are continuouslyformed to function as a conductive path and to reduce the volumeresistivity of the ceramics.

[0026] The volume resistivity of a normal boron nitride is relativelyhigh and not lower than 10¹⁶ Ω·cm. If the boron nitride phases arecontinuous to from a network microstructure, it should be difficult toreduce the volume resistivity of an aluminum nitride ceramics.

[0027] The inventors have measured the distribution of each element ineach of aluminum nitride sintered bodies in the examples describedlater. As a result, it is found that the intergranular phase is mainlyconsisting of boron nitride and also contains carbon atoms.

[0028] Boron nitride has hexagonal crystalline system as carbon(graphite). The peaks of boron nitride are near to those of graphitemeasured by X-ray diffraction analysis. Carbon has, however, spacings ofcrystal lattices larger than those of boron nitride. For example, aspacing d004 of 004 diffraction peak of boron nitride is 1.6636 angstromaccording to No. 34-0421. The peak position of carbon corresponding tod004 of boron nitride is 0012 of JCPDS No. 26-1076. d0012 is 1.6740angstrom.

[0029] On the contrary, the ceramics according to the present inventionhas a spacing d004 of 004 diffraction peak of boron nitride of not lowerthan 1.6650 angstrom. The value is considerably larger than d004 ofnormal boron nitride and smaller than d0012 of carbon. That is, in theinventive ceramics, the intergranular phase consists of boron nitridewhose crystal lattice is larger than that of normal boron nitride andsmaller than that of carbon.

[0030] The expansion of crystal lattice shows that carbon atoms aresolid-soluted into crystalline lattices of boron nitride constitutingthe intergranular phase of an aluminum nitride ceramics. The resistivitymay thus be reduced considerably. The intergranular phases with areduced resistivity are made continuous to function as an electricallyconductive path, so that the volume resistivity of the ceramics may beconsiderably reduced.

[0031] When boron carbide is added to raw material of aluminum nitrideand the mixed powder is sintered, boron carbide reacts with gaseousnitrogen to generate boron nitride in grain boundaries between aluminumnitride grains during the sintering. During the process, a part ofcarbon atoms is solid-soluted into boron nitride and left in theintergranular phase.

[0032] The inventors have further added boron nitride powder directlyinto raw material of aluminum nitride and sintered the mixed powder.Also in this case, intergranular phases mainly consisting of boronnitride are formed in grain boundaries of aluminum nitride grains. Inthis case, however, carbon atoms are not solid-soluted intointergranular phases and the expansion of spacings accompanied with thesolid-soluted carbon atoms is not observed. Even when a large amount ofboron nitride is added, the volume resistivity of the ceramics is higherthan 10¹⁵ Ω·cm and not reduced. The results show that the intergranularphase itself does not have an electrical conductivity and does notfunction as a conductive path.

[0033] Further, in Japanese patent publication 5-178, 671A, boroncarbide (B₄C) in an amount of 0.5 weight percent calculated as boron isadded into aluminum nitride powder and the mixed powder is then sinteredat 1800° C. for two hours. It is thus obtained a sintered body having athermal conductivity of 153 W/m·k and a relative porosity of 98.9percent. Boron carbide is added as a second additive for helping thesintering process of aluminum nitride powder at atmospheric pressure.The addition of boron carbide is said to have the effects of reducingthe crystalline growth. It is thereby obtained a sintered body having ahigh thermal conductivity, an improved surface roughness and reducedcolor defects or irregularities. The relationship between the additionof boron carbide and volume resistivity is not described. According tothe study of the inventors, the inventive ceramics cannot be producedaccording to the conditions and composition disclosed in the patent.

[0034] These and other objects, features and advantages of the inventionwill be appreciated upon reading the following description of theinvention when taken in conjunction with the attached drawings, with theunderstanding that some modifications, variations and changes of thesame could be made by the skilled person in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a backscattering electron image taken by a scanningelectron microscope of a polished surface of a sample according toexample 1 for the analysis of microstructure.

[0036]FIG. 2 is a backscattering electron image taken by a scanningelectron microscope of a polished surface of a sample according toexample 2 for the analysis of microstructure.

[0037]FIG. 3 is a backscattering electron image taken by a scanningelectron microscope of a polished surface of a sample according tocomparative example 1 for the analysis of microstructure.

[0038]FIG. 4 shows a photograph taken by an atomic force microscopeshowing the current distribution analysis image of a sample according toexample 1.

[0039]FIG. 5 shows a photograph taken by an atomic force microscopeshowing the surface roughness of a sample according to example 1 overthe same visual field as FIG. 4.

[0040]FIG. 6 is a photograph of element distribution analysis of asample according to example 1 by EPMA.

PREFERRED EMBODIMENTS OF THE INVENTION

[0041] An aluminum nitride ceramics according to the present inventionmeans a ceramic material mainly consisting of a polycrystalline bodycomposed of aluminum nitride. The ceramics may be produced by a processnot particularly limited, including a gaseous phase process such aschemical vapor deposition, physical vapor deposition, organic metalchemical vapor deposition and vapor deposition. The aluminum nitrideceramics may preferably be produced by sintering.

[0042] The content of aluminum in the aluminum nitride sintered bodyshould be enough for forming aluminum nitride as the main phase. Thecontent may preferably be not lower than 35 weight percent, and morepreferably be not lower than 50 weight percent, of the sintered body.

[0043] The content of aluminum nitride may preferably be not lower than80 weight percent and more preferably be not lower than 90 weightpercent.

[0044] It is preferred to increase the content of boron atoms to a valuenot lower than 1.0 weight percent and the content of carbon atoms to avalue not lower than 0.3 weight percent in an aluminum nitride ceramics.The formation of continuous intergranular phases may be thereby promotedso as to further reduce the volume resistivity of an aluminum nitrideceramics. On this viewpoint, the content of boron atoms may preferablybe not lower than 2.0 weight percent, or, the content of carbon atomsmay preferably be not lower than 0.5 weight percent.

[0045] The thermal conductivity of an aluminum nitride ceramics may befurther increased by reducing the content of boron atoms to a value nothigher than 5.0 weight percent. On this viewpoint, the content of boronatoms may preferably be not higher than 4.0 weight percent.Alternatively, the thermal conductivity of an aluminum nitride ceramicsmay be increased by reducing the content of carbon atoms to a value nothigher than 1.5 weight percent. On this viewpoint, the content of carbonatoms may more preferably be not higher than 1.0 weight percent.

[0046] In a preferred embodiment, the ratio of the contents (by weight)of carbon atoms to boron atoms (C/B) is controlled at a value not lowerthan 0.2 and not higher than 0.4. It is thereby possible to furtherreduce the volume resistivity of an aluminum nitride ceramics.

[0047] An aluminum nitride ceramics according to the present invention,particularly sintered body, may preferably contain a rare earth elementin an amount of 0.2 to 10 weight percent. It is thereby possible toobtain a dense body at a lower sintering temperature compared with theceramics with no rare earth element added. The addition of a rare earthelement also has the effects of promoting the growth of intergranularphases and improving the thermal conductivity. For further promoting thesintering, the content of rare earth element may preferably be not lowerthan 0.2 weight percent and more preferably be not lower than 0.5 weightpercent. For improving the thermal conductivity, the content of a rareearth element may preferably be not higher than 10 weight percent.

[0048] The rare earth element refers to the following seventeenelements; samarium, scandium, yttrium, lanthanum, cerium, praseodymium,neodymium, promethium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium and lutetium.

[0049] In a preferred embodiment, the rare earth element is one or moreelement selected from the group consisting of yttrium, lanthanum,cerium, neodymium, samarium, gadolinium, dysprosium, erbium andytterbium.

[0050] For providing a corrosive resistant sintered body suited forapplications in which the contamination of impurities is to be highlycontrolled (such as an application for producing semiconductors), thetotal content of metal elements (excluding aluminum and rare earthelements) may preferably be not higher than 100 ppm, in some cases. Thetotal content may more preferably be not higher than 50 ppm.

[0051] In a preferred embodiment, the open porosity of an aluminumnitride ceramics is not higher than 1 percent and more preferably be nothigher than 0.1 percent.

[0052] In a preferred embodiment, the thermal conductivity of analuminum nitride ceramics according to the present invention is notlower than 30 W/m·K. The upper limit of the thermal conductivity is notlimited and may usually be 170 W/m·K and especially 150 W/m·K.

[0053] In a preferred embodiment, an aluminum nitride ceramics containsintergranular phases mainly consisting of boron nitride. The followingcrystalline phases may be generated other than boron nitride phase. Ithas been proved that these secondary crystalline phases do notsubstantially affect the resistivity of an aluminum nitride ceramics.

[0054] (1) A complex oxide phase of a rare earth element and aluminum,such as Y₃Al₅O₁₂ (YAG), YAlO₃ (YAL), Y₄Al₂O₉ (YAM)

[0055] (2) A boride of a rare earth element such as ReB₄ (“Re”represents a rare earth element) and ReB₆

[0056] (3) A borocarbide of a rare earth element such as ReB₂C₂

[0057] (4) An oxide of a rare earth element such as Re₂O₃

[0058] In a preferred embodiment, the intergranular phase is formedalong the outer face of aluminum nitride particle and plate-shaped orfilm-shaped. In a still preferred embodiment, the intergranular phasehas an elongate shape preferably of an aspect ratio of not lower than 5,viewed on a ground face of an aluminum nitride ceramics in a magnitudeof 500 to 1000.

[0059] In a preferred embodiment, the intergranular phases formthree-dimensional network. In this embodiment, it is not needed that theintergranular phases are continuous over the whole of an aluminumnitride ceramics. It is needed, however, that intergranular phases arecontinuous over plural aluminum nitride grains.

[0060] The conductive path constituted by the intergranular phase may beconfirmed by taking a photograph by an atomic force microscope showingthe current distribution analysis image of the ceramics and by measuringthe contrast of the lightness of aluminum nitride grains and that of theintergranular phase.

[0061] Preferably, the spacing d004 of 004 diffraction peak of theintergranular phase is not lower than 1.6650 angstrom. d004 may morepreferably be not lower than 1.6653 angstrom and most preferably be notlower than 1.6656 angstrom. d004 is not higher than 1.6740 angstrom(d0012 of carbon) and usually not higher than 1.6730 angstrom.

[0062] In a preferred embodiment, the aluminum nitride ceramicsaccording to the present invention has a ratio of volume resistivity atroom temperature to that at 500° C. of 0.01 to 100. The presentinvention successfully provides an aluminum nitride ceramics having anextremely small dependency of volume resistivity on temperature. Theconductive phase of the inventive ceramics has a high electricalconductivity to give metallic properties. The ceramic according to thepresent invention having a reduced temperature dependency of resistivityis particularly useful as a base material of, for example, anelectrostatic chuck.

[0063] In the ceramics according to the present invention, the ratio ofvolume resistivity at room temperature to that at 500° C. may morepreferably be 0.5 to 50 and particularly preferably be 0.1 to 10.

[0064] In a preferred embodiment, an aluminum nitride ceramics hasaluminum nitride and plate-like intergranular phases mainly consistingof boron nitride. The intergranular phase has a length of one side ofnot shorter than 5 μm. It is thereby possible to further reduce thedependency of volume resistivity on temperature. In this embodiment, theintergranular phase has a longer side, meaning that the enhancement ofgrowth of intergranular phase. In this case, the crystallinity of theintergranular phase is further improved, so that electrons may movefreely or with less bindings. Therefore, the intergranular phase has ahigher electrical conductivity and behaves like a metal concerning thetemperature dependency of volume resistivity. On the other hand, it ispossible to increase the volume resistivity of the whole ceramics whilemaintaining the metallic behavior concerning the temperature dependencyof volume resistivity by controlling the content and the degree ofcontinuity of the conductive intergranular phase.

[0065] The raw material of aluminum nitride may be produced by variousprocesses, including direct nitriding, reduction nitriding and gaseousphase synthesis from an alkyl aluminum.

[0066] Boron carbide may be added to raw material of aluminum nitride.When a rare earth element is added, the oxide of a rare earth elementmay be added to the raw material. Alternatively, the compound of a rareearth element forming a rare earth oxide upon heating (a precursor of arare earth oxide) may be added to the raw material. The precursorincludes a nitrate, sulfate, oxalate and alkoxide. The precursor may beadded as powder. The precursor such as a nitrate or sulfate may bedissolved into a solvent to obtain solution, which may be added into theraw material. It is thereby possible to uniformly disperse atoms of therare earth element between aluminum nitride particles by dissolving theprecursor in a solvent.

[0067] The raw material may be shaped by any known methods including drypress, doctor blade, extrusion, casting and tape forming methods.

[0068] In a formulating step, raw powder of aluminum nitride may bedispersed in a solvent, into which the rare earth element may be addedin a form of powder of the rare earth oxide or the solution describedabove. In a mixing step, it is possible to simply stir the formulation.When the raw powder contains aggregates, it is possible to use a mixingand pulverizing machine, such as a pot mill, trommel and attrition mill,for pulverizing the aggregates. When using an additive soluble in asolvent for pulverizing, it is enough to carry out the mixing andpulverizing step for a short (minimum) time. Further, a bindercomponent, such as polyvinyl alcohol, may be added. In a step ofremoving a binder, however, it is necessary to avoid the shift or changeof the formulation due to the oxidation of boron carbide.

[0069] The solvent used for the mixing step may be dried, preferably byspray dry method. After carrying out vacuum drying process, the particledistribution of the dried particles may preferably be adjusted bypassing the particles through a mesh.

[0070] In a forming step of the powdery material, the material may bepressed using a metal mold to provide a disk-shaped body. The pressurefor pressing raw material is not particularly limited, as long as theformed body may be handled without causing any fracture. The pressuremay preferably be not lower than 100 kgf/cm². The powdery material maybe supplied into a die for hot pressing without particularly forming thepowdery material.

[0071] The sintered body according to the invention may preferably beproduced by hot pressing a body to be sintered, preferably at a pressureof not lower than 50 kgf/cm².

[0072] The sintering temperature is not limited, and may preferably be1700 to 2200° C. and more preferably be not lower than 1750° C. or nothigher than 2100° C. The sintering temperature may most preferably be1750 to 2050° C.

[0073] In a sintering step, the temperature may preferably be held at aholding temperature between 1400 to 1800° C. before sintering at amaximum temperature. It is proved that the growth of the intergranularphases mainly consisting of boron nitride in the sintered body may befurther progressed to make the intergranular phases continuous and tofurther reduce the volume resistivity, by adding this temperatureholding step.

[0074] The preferred holding temperature in the temperature holding stepmay be changed depending on the added amount of boron carbide. Theholding temperature may generally preferably be not lower than 1450° C.and not higher than 1750° C. It is possible to control the values ofvolume resistivity and thermal conductivity by adjusting the holdingtemperature. For example, the holding temperature may preferably be 1550to 1650° C. for controlling the volume resistivity at a value not higherthan 100 Ω·cm. The holding temperature may preferably be 1450 to 1550°C. for controlling the resistivity at a value between 10⁵ and 10¹² Ω·cm.The holding temperature may preferably be 1650 to 1750° C. forcontrolling the resistivity at a value between 100 and 10⁷ Ω·cm. Forimproving the thermal conductivity, the holding temperature maypreferably be higher.

[0075] Besides, during the temperature holding step, it is possible tochange the holding temperature. For example, the raw material may beheld at 1500° C. for a specified time period and then held at 1550° C.Alternatively, the temperature may be slowly elevated from 1500 to 1800°C. The time period for the temperature holding step may preferably benot shorter than 2 hours and more preferably be not shorter than 4hours.

[0076] The aluminum nitride ceramics according to the invention maypreferably be used for various members in a system for producingsemiconductors, such as systems for treating silicon wafers and formanufacturing liquid crystal displays. Such system for producingsemiconductors means a system usable in a wide variety of semiconductorprocesses in which metal contamination of a semiconductor is to beavoided. Such system includes a film forming, etching, cleaning andtesting systems.

[0077] An aluminum nitride ceramics according to the invention may beused as a corrosion resistant member. The corrosion resistant member maybe used against corrosive substances such as a liquid including nitricacid, hydrochloric acid, mixed acid, hydrofluoric acid and aqua regia.The corrosive substance further includes a chlorine-based corrosive gassuch as Cl₂, BCl₃, ClF₃, HCl or the like and a fluorine-based corrosivegas such as ClF₃ gas, NF₃ gas, CF₄ gas, WF₆, SF₄ or the like. Thecorrosion resistant member is particularly useful against the plasma ofeach gas.

[0078] The member for a system for producing semiconductors maypreferably be a corrosion resistant member such as a susceptor for thesystem. The inventive ceramics may be preferred for a metal embeddedarticle having a corrosion resistant member and a metal member embeddedtherein. The corrosion resistant member includes a susceptor formounting a semiconductor wafer thereon, a dummy wafer, a shadow ring, atube for generating high frequency plasma, a dome for generating highfrequency plasma, a high frequency wave-permeable window, an infraredradiation-permeable window, a lift pin for supporting a semiconductorwafer, a shower plate, an electrostatic chuck and a vacuum chuck. Aresistive heating element, electrostatic chuck electrode or an electrodefor generating high frequency plasma may be embedded in the susceptor.

[0079] An aluminum nitride ceramics according to the present inventionmay be used as a conductive material having a volume resistivity at roomtemperature of not higher than 10⁶ Ω·cm. It has been not known aconductive ceramic material having excellent corrosion resistantproperty and thermal conductivity as described above. The presentinvention thus provides a novel conductive ceramics having highcorrosion resistant property. The volume resistivity may more preferablybe reduced to a value not higher than 100 Ω·cm.

[0080] Such conductive member may be utilized as, for example, a counterelectrode for generating high frequency for use in a system forproducing semiconductors. The conductive member may also be utilized asan electrode or heat generator to be exposed against a halogen-based gasor various chemical substances.

EXAMPLES

[0081] (1) Production of Mixed Powder of AlN/B₄C/Y₂O₃

[0082] Commercial AlN powder produced by reduction nitriding (oxygencontent of 0.97 weight percent) was used. Commercial B₄C powder having ahigh purity and a mean particle diameter of 1.5 μm was used. Commercialpowder of Y₂O₃ with a purity of not lower than 99.9 percent and a meanparticle diameter of not larger than 1 μm was used.

[0083] Each powder was weighed as shown in tables 1 to 5. The amounts ofB₄C and Y₂O₃ were converted to weight parts provided that the amount ofaluminum nitride was converted to 100 weight parts. Each weighed powderwas then subjected to wet blending using isopropyl alcohol as a solvent,a nylon pot and nylon media for 4 hours to obtain slurry. After theblending, the slurry was collected and dried at 110° C. in nitrogenatmosphere to obtain powdery raw material. The amounts of AlN, B₄C andY₂O₃ in the formulation were calculated as “weight parts” ignoring thecontents of impurities in each powder.

[0084] (2) Forming and Sintering Steps

[0085] Each mixed powder obtained in (1) section was then formed byuniaxial pressing at a pressure of 200 kgf/cm² to obtain a disk-formedbody with a diameter of about 50 mm and a thickness of about 20 mm,which was then contained in a mold made of graphite for sintering.

[0086] Each formed body was sintered by hot pressing at a pressure of200 kgf/cm². In the sintering step, the temperature was risen at a speedof 300 to 1000° C./hour and then held at each holding temperature shownin tables 1 and 3 for 20 hours. The temperature was then risen to amaximum temperature of 1800 to 2000° C., then held for 4 hours and thencooled. In the cooling step, the temperature was lowered to 1400° C. ata speed of 300° C./hour and then cooled in a furnace. During thesintering, the formed body was set in vacuum from room temperature to1000° C. and nitrogen gas was then introduced at a pressure of 1.5 MPaat 1000° C. The pressure was then held at 0.15 MPa until the temperaturereached 1400° C. in the cooling step while nitrogen gas was introducedat a flow rate of 5 liter/minute.

[0087] (3) Evaluation

[0088] The thus obtained sintered bodies were subjected to the followingevaluation.

[0089] (Density, Open Porosity)

[0090] They are measured by Archimedes' method using water as a medium.

[0091] (Volume Resistivity)

[0092] It is measured by a method according to “JIS C 2141” at roomtemperature under air, in samples having a volume resistivity of notlower than 106 Ω·cm. The test sample has the following parts: a circularplate with a diameter ø of 50 mm and thickness of 1 mm; a main electrodewith a diameter of 20 mm; a guard electrode with an inner diameter of 30mm and outer diameter of 40 mm; and an applying electrode with adiameter of 45 mm. The electrodes are formed of silver. 100 V/mm ofvoltage is applied and a current is read one minute after theapplication of voltage so that the volume resistivity is calculated.

[0093] The resistivity is measured by four probe method in a samplehaving the resistivity of lower than 106 Ω·cm.

[0094] The volume resistivities at 100, 300 and 500° C. are alsomeasured.

[0095] (Bending Strength)

[0096] A four-point bending strength at room temperature is measuredaccording to “JIS R1601”.

[0097] (Thermal Conductivity)

[0098] Thermal conductivity was measured by laser flash method andcalculated. The specific heat value (753 kJ/kg·K) of aluminum nitridewas applied for the calculation.

[0099] (Contents of B and Y)

[0100] They are determined by inductively coupled plasma (ICP)spectrometry.

[0101] (Oxygen and Nitrogen Contents)

[0102] They are determined by inert gas melting infrared absorptiometryanalysis method.

[0103] (Carbon Content)

[0104] It is determined by high frequency heating infraredabsorptiometry analysis method.

[0105] (Crystalline Phase)

[0106] It is determined by using a rotating anode type X-ray diffractionsystem “RINT” supplied by “Rigaku Denki” under the following condition:CuK α, 50 kV, 300 mA, and 2θ=20 to 70°.

[0107] (Observation of Microstructure)

[0108] The polished surface of a sample was observed by backscatteringelectron image. It is also analyzed by EPMA and an atomic forcemicroscope (AFM). TABLE 1 B₄C Y₂O₃ sintering holding open apparent bulkamount added amount added temperature temperature porosity densitydensity volume resistivity example parts by weight parts by weight ° C.(° C.) % g/cm³ g/cm³ room temperature 100° C. 300° C. 500° C. 1 3.4 22000 1600 0.02 3.19 3.18 1.9 — — — 2 5.7 2 2000 1600 0.04 3.13 3.13 1 —— — 3 3.4 0 2000 1600 0.04 3.17 3.17 3E+06 3E+06 9E+05 5E+05 4 2.3 22000 1600 0.04 3.22 3.22 19 — — — 5 3.4 5 2000 1600 0.01 3.19 3.19 8.7 —— — 6 3.4 0.5 2000 1600 0.01 3.16 3.16 830000 7E+05 2E+05 1E+05 7 3.4 22000 1700 0.02 3.18 3.17 2E+06 2E+06 1E+06 6E+05 8 3.4 5 2000 1700 0.013.17 3.17 5800 — — — 9 4.6 2 2000 1600 0.03 3.16 3.16 1.5 — — —

[0109] TABLE 2 bending thermal chemical analysis strength conductivity BN O C Y C/B weight identified example MPa W/mK wt % wt % wt % wt % wt %ratio intergranular phase 1 279 56 2.40 33.62 1.05 0.74 1.29 0.31 BN,YAL 2 268 33 3.90 33.61 1.15 1.14 1.40 0.29 BN, YAM 3 401 55 . . . . . .BN, B₄C 4 298 67 1.68 33.40 0.95 0.55 1.09 0.33 BN, YAL 5 282 80 . . . .. . BN, YAM 6 389 61 . . . . . . BN, YAL 7 351 104 . . . . . . BN, YAL 8317 135 . . . . . . BN, YAM 9 227 52 . . . . . . BN, YAL

[0110] TABLE 3 B₄C Y₂O₃ sintering holding open apparent bulk amountadded amount added temperature temperature porosity density densityvolume resistivity example parts by weight parts by weight ° C. (° C.) %g/cm³ g/cm³ room temperature 100° C. 300° C. 500° C. 10 5.7 0 2000 15000.05 3.13 3.13 4E+06 2E+06 2E+05 7E+04 11 5.7 2 2000 1500 0.01 3.14 3.146E+08 — — — 12 5.7 5 2000 1500 0.02 3.17 3.17 2E+08 1E+08 3E+07 7E+06 135.7 0 2000 1600 0.01 3.11 3.11 78 — — — 14 5.7 5 2000 1600 0.01 3.153.15 0.86 — — — 15 5.7 2 2000 1700 0.00 3.12 3.12 8300 — — — 16 5.7 52000 1700 0.00 3.12 3.12 21 — — — 17 5.7 2 1900 1500 0.00 3.12 3.122E+11 3E+10 6E+08 4E+07 18 B₄C: 1.1 2 2000 1600 0.00 3.24 3.24 9E+059E+05 9E+05 1E+06    C: 0.5 19 1.5 5 1900 1600 0.00 3.25 3.25 6E+077E+07 9E+07 6E+07

[0111] TABLE 4 bending thermal chemical analysis strength conductivity BN O C Y C/B weight identified intergranular example Mpa W/mK wt % wt %wt % wt % wt % ratio phase 10 448 41 4.08 32.51 0.82 1.26 0.00 0.31 BN,B₄C 11 325 43 3.79 32.78 1.20 1.14 1.00 0.30 BN, YB₄ 12 342 43 3.8632.17 1.49 1.13 3.07 0.29 BN, YB₄, YAL, YB₂C₂ 13 336 43 . . . . . . BN,B₄C 14 263 53 . . . . . . BN, YAM 15 346 63 . . . . . . BN, YAM 16 300116 . . . . . . BN, YAM, Y₂O₃ 17 464 36 . . . . . . BN, YB₄ 18 337 93 .. . . . . BN, YAL 19 359 125 . . . . . . BN, YAM

Example 1

[0112] The powdery raw material has a composition of 100/3.4/2.0(AlN/B₄C/Y₂O₃; weight parts). The raw material was formed and sintered.In the sintering step, the temperature was risen at a speed of 1000°C./hour, held at 1600° C. for 20 hours and held at 2000° C. for 4 hoursto obtain a dense body. The pressure during the sintering step was heldat 0.15 MPa. The sintered body was processed for the evaluation ofproperties shown in the tables.

[0113] The sintered body has a bulk density of 3.19 g/cm³ and an openporosity of not higher than 0.1 percent to indicate that the body issufficiently densified. The resistivity at room temperature measured byfour probe method is 1.9 Ω·cm and is surprisingly low value. The fourpoint bending strength is 279 MPa and thermal conductivity is 56 W/mK,both values being high.

[0114] It is proved that the sintered body has, in addition to AlNphase, YAlO₃ (YAL) phase and a phase mainly consisting of BN. In thissample, although B₄C is added into raw material, the diffraction peakcorresponding to B₄C is not observed.

[0115] The distribution of the plate-like phase is identical with thatof B atoms according to the mapping by means of EPMA (FIG. 6). It isthus proved that the plate-like phase is mainly consisting of BN. It isalso proved that the plate-like phase further contains carbon atoms.

Example 2

[0116] The powdery raw material has a composition of 100/5.7/2.0(AlN/B₄C/Y₂O₃; weight parts). The raw material was shaped and sinteredunder the same conditions as the example 1. The properties of thesintered body were evaluated.

[0117] The sintered body has a bulk density of 3.13 g/cm³ and an openporosity of not higher than 0.1 percent to indicate that the body issufficiently densified. The resistivity at room temperature measured byfour probe method is 1 Ω·cm and is surprisingly low value. The fourpoint bending strength is 268 MPa and thermal conductivity is 33 W/mK.It is proved that the sintered body has, in addition to AlN phase,Y₄A₂O₉ (YAM) phase and a phase mainly consisting of BN by X-raydiffraction analysis.

Examples 3 to 17

[0118] In example 3, the same conditions as the example 1 are appliedexcept that yttria is not added. As a result, the volume resistivity is3×10⁶ Ω·cm. In the example 1, the volume resistivity is extremelyreduced to 1.9 Ω·cm by the addition of yttria. The addition of yttria isthus proved to be effective for further reducing the volume resistivity.Moreover, although B₄C phase is not identified in the example 1 with theaddition of yttria, B₄C phase is identified in the example 3 without theaddition of yttria. These results are consistent with a theory that theaddition of yttria may assist the conversion of B₄C to BN in thesintered body.

[0119] In example 4, substantially same results as the example 1 areobtained. Since an amount of the added B₄C is slightly lower (2.3 weightpercent) in the example 4, the volume resistivity is slightly higherthan that in the example 1.

[0120] In each of examples 5 to 9, amounts of B₄C, yttria and holdingtime periods are variously changed. The experimental results aresubstantially in conformity with those in the examples 1 to 4.

[0121] In examples 10 to 17, an amount of B₄C is set at 5.7 weightpercent and an amount of yttria, maximum temperature in the sinteringstep and holding temperature are variously changed. These results arealso in conformity with the above results. It is also proved that thevolume resistivity may be further reduced by increasing the amount ofB₄C added to raw material.

[0122] Further as can be seen from the above results, the holdingtemperature in the temperature holding step may preferably be 1450 to1750° C. and the maximum temperature may preferably be not lower than1800° C. The holding temperature may preferably be 1550 to 1650° C. forreducing the volume resistivity to a value not higher than 100 Ω·cm. Theholding temperature may preferably be 1450 to 1550° C. for reducing thevolume resistivity at a value between 10⁵ to 10¹² Ω·cm. The holdingtemperature may preferably be 1650 to 1750° C. for reducing the volumeresistivity of 100 to 10⁷ Ω·cm. It is possible to control the growth ofthe intergranular phases mainly consisting of BN by controlling theholding temperature. Especially the holding temperature of 1550 to 1650°C. may be effective for the growth of the plate-like and continuousintergranular phases and for enhancing the solid solution of carbonatoms into the intergranular phases. It is thus preferred for obtaininga ceramics having a lower volume resistivity.

[0123] The preferred ranges of resistivity and holding temperature aresome of examples. The preferred holding temperature range for thecorresponding resistivity range may be varied depending on an amount ofadded B₄C.

[0124] Moreover in the example 3, the ratio of the volume resistivity atroom temperature to that at 500° C. is about 10 times. In the examples 6and 7, the ratio of the volume resistivity at room temperature to thatat 500° C. is lower than 10 times. In the examples 10 and 12, the ratioof the volume resistivity at room temperature to that at 500° C. isabout 60 or 30 times. It is thus obtained the sintered body having a lowvolume resistivity at room temperature as well as a smaller differencebetween the volume resistivities at room temperature and 500° C.

Example 18

[0125] In example 18, commercial carbon powder having a high purity wasadded as well as B₄C and Y₂O₃. The powdery raw material has acomposition of 100/1.1/2.0/0.5 (AlN/B₄C/Y₂O₃/C ;weight parts). In thesintering step, the shaped body was held at 1600° C. for 20 hours andthen held at 2000° C. for 4 hours. The other conditions are the same asthe example 1.

[0126] In the sintered body according to the example 18, a small amountof added carbon may be contained in the conductive phase and functionssubstantially same as B₄C. The sintered body has a considerably lowvolume resistivity at room temperature. Further, the volume resistivityat 500° C. is substantially the same as that at room temperature. Thesurprising results may be caused as follows. In the example, arelatively small amount of B₄C is added. The amount of liquid phasegenerated in the sintering step is relatively large compared with theamount of B₄C so that B, C and O atoms may be easily diffused to enhancethe growth of the conductive phase mainly consisting of boron nitride.

Example 19

[0127] In example 19, the powdery raw material has a composition of100/1.5/5.0 (AlN/B₄C/Y₂O₃;weight parts). In the sintering step, thetemperature was held at 1600° C. for 20 hours and then held at 1900° C.for 4 hours. The other conditions are the same as the example 1.

[0128] The sintered body according to the example 19 has a considerablylow volume resistivity at room temperature. Further, the volumeresistivity at 500° C. is substantially the same as that at roomtemperature. The surprising results may be caused as follows. In theexample, a relatively small amount of B₄C is added. The amount of liquidphase generated in the sintering step is relatively large compared withthe amount of B₄C so that B, C and O atoms may be easily diffused toenhance the growth of the conductive phase mainly consisting of boronnitride.

Comparative Example 1

[0129] Commercial BN powder having a high purity was used instead of B₄Cand the sintered body was evaluated. The powdery raw material has acomposition of 100/32.9/2.0 (AlN/BN/Y₂O₃ ;weight parts). The temperaturewas risen at a speed of 1000° C./hour. The formed body was held at 1600°C. for 20 hours and then held at 2000° C. for 4 hours to produce a densebody. The pressure was held at 0.15 MPa in the sintering step.

[0130] It is obtained a sufficiently dense body having a volumeresistivity at room temperature of as high as 1×10¹⁵ Ω·cm. BN and YAlO₃phases are identified in addition to AlN phase by X-ray diffractionmeasurement.

Comparative Example 2

[0131] A dense body was produced under the conditions same as those inthe comparative example 1 except that the powdery raw material has acomposition of 100/8.5/2.0 (AlN/BN/Y₂O₃; weight parts). The volumeresistivity at room temperature and identified phases are the same asthose in the comparative example 1. TABLE 5 BN Y₂O₃ sintering holdingOpen Apparent bulk volume resistivity bending Thermal comparative amountadded amount added temperature temperature porosity density density Ω ·cm at strength conductivity example parts by weight parts by weight ° C.° C. % g/cm³ g/cm³ room temperature Mpa W/mK 1 32.9 2 2000 1600 0.022.93 2.93 1E+15 332 64 2 8.5 2 2000 1600 0.02 3.16 3.16 1E+15 382 113comparative B N O C Y weight ratio identified example wt % wt % wt % wt% wt % C/B intergranular phase 1 10.56 38.88 1.22 0 04 1.55 0.00 BN YAL2 3.35 35.19 1.22 0.04 1.55 0.01 BN YAL

[0132] (Comparison of Microstructure of Samples According to theExamples 1, 2 and Comparative Example 1)

[0133]FIGS. 1, 2 and 3 are photographs showing backscattering electronimages of polished surfaces of samples according to the examples 1, 2and comparative example 1 for the analysis of the microstructure. InFIGS. 1, 2 and 3, each photograph may be roughly divided into threeregions in terms of brightness: white, gray and black regions.

[0134] The white region corresponds with intergranular phase containingY atoms and having a dimension of submicrons to several microns. Thegray region is consisting of AlN phase constituting matrix of eachsintered body. The black region is plate-like intergranular phase thatis proved to be mainly consisting of BN according to the results ofX-ray diffraction analysis and element analysis by EPMA. In the sampleaccording to the example 1, this blackish intergranular phase is grown,so that adjacent plate-like intergranular phases are interconnected witheach other to form a kind of network. In the sample according to theexample 2 with a larger amount of B₄C added, AlN particles (gray region)are smaller than those in the sample according to the example 1 and theblackish intergranular phase mainly consisting of BN are interconnectedto form a kind of network microstructure. In the sample according to thecomparative example 1, the content of BN is very large and BN phases areinterconnected at many points. However, the growth and formation ofplate like pattern is not clearly observed.

[0135] (Mechanism for the Reduced Resistivity in the Sample According tothe Example 1)

[0136] The relationship between the microstructure (especiallyintergranular phase) and the resistivity of the sample according to theexamples 1, 2 or comparative example 1 was further investigated asfollows. The sample according to the example 1 having a reducedresistivity was analyzed by means of an atomic force microscope (AFM) toobtain a current distribution analytic images, which is shown in FIG. 4.The analysis was carried out using a model “SPM stage D 3100” (probetype“DDESP”) supplied by Digital Instruments. The test sample has ashape of a plate. The surface of the sample was polished for currentdistribution analysis. A DC bias was applied on the back face of thesample. The measurement of current distribution on the surface wasperformed on contact AFM current measurement mode. FIG. 5 is an imageshowing the surface roughness over the same visual field as that of FIG.4. The shape of each grain may be observed in this image. In FIG. 4, thecurrent is larger in a white and bright region, indicating that theconductivity is high. As can be seen from the figures, the conductivephase (white and bright region) is elongated to have a plate-like shape.The distribution and shape of the conductive phase (shown in FIG. 4) isproved to be identical with the distribution of the plate-likeintergranular phase shown in FIG. 5. It is also confirmed that thedistribution of the conductive phase (blackish region) is identical withthe distribution of the intergranular phase mainly consisting of BNshown in FIG. 1.

[0137] Therefore, the intergranular phases mainly consisting of BN havea low resistivity and three-dimensionally interconnected to formconductive path or network to reduce the resistivity of the sample. Inthe comparative example 1 shown in FIG. 3, although the intergranularphases mainly consisting of BN are continuous, the intergranular phasehas a higher resistivity (contrary to the example 1) to prevent thereduction of the resistivity of the sample.

[0138] (Analysis of the Intergranular Phase Mainly Consisting of BN)

[0139]FIG. 6 shows the results of analyzing the distribution of elementsby EPMA for the sample according to the example 1. B, C and N atoms aredetected in the plate-like intergranular phase mainly consisting of BN.Although BN of hexagonal crystalline system usually has a highresistivity, it is proved that the intergranular phase mainly consistingof BN further contains C component. The C component is solid-solutedinto BN phase to reduce the resistivity of BN otherwise having a higherresistivity.

[0140] The positions of diffraction peaks were investigated by X-raydiffraction measurement for further analysis of the intergranular phasemainly consisting of BN. 004 peak (JCPDS No. 34-0421: 2θ=55.164°)without overlapping the other peaks is applied as a peak correspondingwith BN. Al₂O₃ having known lattice constants is added as an internalstandard. The deviation of the 116 peak (2θ=57.497°) is used to adjustthe 2θ position of the 004 peak of BN. 2θ is measured by peak top methodto calculate the spacing d004 value of the 004 diffraction peak. As aresult, in the sample according to the example 1, d004 is proved to be1.6683 angstrom, which is considerably larger that that of BN (JCPDS No.34-0421: 2θ=55.164°; d004 is 1.6636 angstrom). That is, the lattice ofthe intergranular phase mainly consisting BN in the sample according tothe example 1 is expanded compared with the lattice of normal BN.

[0141] C (graphite) has the basic crystalline structure same as that ofhexagonal BN. The diffraction pattern and peak positions of graphite byX-ray diffraction measurement are also very similar to those ofhexagonal BN. d004 of BN corresponds with d0012 of C (JCPDS No.26-1076:2θ=54.7930°; d0012 is 1.6740 angstrom). That is, the above peak of Ccorresponding with d004 of BN has a slightly larger spacing. The spacingof the sample according to the example 1 is compared with those of BNand C and shown in table 6.

[0142] The spacing of the sample according to the example 1 is proved tobe between those of BN and graphite. The results is consistent with thetheory that C component is solid-soluted into BN to expand the crystallattices of BN. The C components solid-soluted into BN phase may providea high conductivity to BN phase to reduce the volume resistivity of thesample.

[0143] The sample according to the example 7 has the same composition asthat in the example 1, except that the holding temperature during thetemperature holding step is 1700° C. and higher than that in theexample 1. The volume resistivity at room temperature is 2×10⁶ Ω·cm inthe example 7. The spacing d004 of the phase mainly consisting of BN is1.6659 angstrom in the example 7. d004 of the sample according to thecomparative example 2 with BN added is 1.6649 angstrom. TABLE 6 J C P DS spacing volume resistivity sample card number (angstrom) (Ω× cm) BNNo. 34-0421 1.6636 comparative — 1.6649 1 × 10¹⁵ example 2 example 7 —1.6659 2 × 10⁶  example 1 — 1.6683 2 C No. 26-1076 1.6740

[0144] As can be seen from the results, the resistivity of the sample isincreased as the spacing d004 of the intergranular phase approaches thatof BN and reduced as the spacing d004 approaches that of graphite. Thatis, the shift of the spacing is clearly correlated with the volumeresistivity. In this way, the resistivity is regulated by the content ofC component solid-soluted into BN phase.

[0145] As described above, the invention may preserve the characteristicproperties of an aluminum nitride and reduce its volume resistivity.

[0146] The present invention has been explained referring to thepreferred embodiments. However, the present invention is not limited tothe illustrated embodiments which are given by way of examples only, andmay be carried out in various modes without departing from the scope ofthe invention.

1. An aluminum nitride ceramics containing boron atoms in an amount ofnot lower than 1.0 weight percent and carbon atoms in an amount of notlower than 0.3 weight percent and having a volume resistivity at roomtemperature of not higher than 1×10¹² Ω·cm.
 2. The ceramics of claim 1,comprising intergranular phases mainly consisting of boron nitride. 3.The ceramics of claim 2, wherein said intergranular phases constitute aconductive path.
 4. The ceramics of claim 2, wherein said intergranularphase is plate-shaped.
 5. The ceramics of claim 2, wherein carbon issolid-soluted into said intergranular phases.
 6. The ceramics of claim1, wherein the ratio (C/B) of carbon atoms to boron atoms by weight isnot lower than 0.2 and not higher than 0.4.
 7. The ceramics of claim 1,containing a rare earth element in an amount of not smaller than 0.2weight percent.
 8. The ceramics of claim 1 having a thermal conductivityof not lower than 30 W/m·K.
 9. The ceramics of claim 1 having an openporosity of not larger than 0.1 percent.
 10. The ceramics of claim 1being a sintered body.
 11. The ceramics of claim 10 being produced bysintering a mixture at least containing aluminum nitride and boroncarbide.
 12. The ceramics of claim 1, wherein the ratio of the volumeresistivity at room temperature to the volume resistivity at 500° C. of0.01 to
 100. 13. A member for use in a system for producingsemiconductors comprising said aluminum nitride ceramics of claim
 1. 14.A corrosion resistant member comprising said aluminum nitride ceramicsof claim
 1. 15. A conductive member comprising said aluminum nitrideceramics of claim
 1. 16. An aluminum nitride ceramics comprisingaluminum nitride and intergranular phases mainly consisting of boronnitride constituting a conductive path and having a volume resistivityat room temperature of not higher than 1×10¹² Ω·cm.
 17. The ceramics ofclaim 16, wherein said intergranular phases constitute a conductivepath.
 18. The ceramics of claim 16, wherein said intergranular phase isplate-shaped.
 19. The ceramics of claim 16, wherein carbon issolid-soluted into said intergranular phases.
 20. The ceramics of claim16, wherein the ratio (C/B) of carbon atoms to boron atoms by weight isnot lower than 0.2 and not higher than 0.4.
 21. The ceramics of claim16, containing a rare earth element in an amount of not smaller than 0.2weight percent.
 22. The ceramics of claim 16 having a thermalconductivity of not lower than 30 W/m·K.
 23. The ceramics of claim 16being a sintered body.
 24. The ceramics of claim 23 being produced bysintering a mixture at least containing aluminum nitride and boroncarbide.
 25. The ceramics of claim 16, wherein the ratio of the volumeresistivity at room temperature to the volume resistivity at 500° C. of0.01 to
 100. 26. A member for use in a system for producingsemiconductors comprising said aluminum nitride ceramics of claim 16.27. A corrosion resistant member comprising said aluminum nitrideceramics of claim
 16. 28. A conductive member comprising said aluminumnitride ceramics of claim
 16. 29. An aluminum nitride ceramicscomprising aluminum nitride and intergranular phases mainly consistingof boron nitride and having a volume resistivity at room temperature ofnot higher than 1×10¹² Ω·cm, wherein 004 diffraction peak of saidintergranular phase has a spacing d004 of not lower than 1.6650angstrom.
 30. The ceramics of claim 29, wherein said intergranular phaseis plate-shaped.
 31. The ceramics of claim 29, wherein saidintergranular phases are continuously formed.
 32. The ceramics of claim29, wherein carbon is solid-soluted into said intergranular phases. 33.The ceramics of claim 29, wherein the ratio (C/B) of carbon atoms toboron atoms by weight is not lower than 0.2 and not higher than 0.4. 34.The ceramics of claim 29, containing a rare earth element in an amountof not smaller than 0.2 weight percent.
 35. The ceramics of claim 29having a thermal conductivity of not lower than 30 W/m·K.
 36. Theceramics of claim 29 having an open porosity of not larger than 0.1percent.
 37. The ceramics of claim 29 being a sintered body.
 38. Theceramics of claim 37 being produced by sintering a mixture at leastcontaining aluminum nitride and boron carbide.
 39. An aluminum nitrideceramics being produced by sintering a mixture at least containingaluminum nitride and boron carbide and having a volume resistivity atroom temperature of not higher than 1×10¹² Ω·cm.
 40. The ceramic ofclaim 39, being produced by holding a mixture at least containingaluminum nitride and boron carbide at a holding temperature not lowerthan 1400° C. and not higher than 1800° C. and then sintered at amaximum temperature higher than said holding temperature.
 41. Theceramics of claim 40, wherein said mixture is held at said holdingtemperature for a time period not shorter than 2 hours.
 42. The ceramicsof claim 39 having a content of aluminum nitride of not lower than 80weight percent.
 43. The ceramics of claim 39, wherein the ratio of thevolume resistivity at room temperature to the volume resistivity at 500°C. of 0.01 to
 100. 44. A member for use in a system for producingsemiconductors comprising said aluminum nitride ceramics of claim 39.45. A corrosion resistant member comprising said aluminum nitrideceramics of claim
 39. 46. A conductive member comprising said aluminumnitride ceramics of claim
 39. 47. A conductive member having a volumeresistivity at room temperature of not higher than 1×10⁶ Ω·cm andcomposed of an aluminum nitride ceramics containing aluminum nitride ina content of not lower than 80 weight percent.
 48. The conductive memberof claim 47 having a volume resistivity at room temperature of nothigher than 100 Ω·cm.
 49. The conductive member of claim 47, whereinsaid aluminum nitride ceramics has intergranular phases mainlyconsisting of boron nitride, said intergranular phases constituting aconductive path.
 50. The conductive member of claim 47, wherein 004diffraction peak of said intergranular phase has a spacing d004 of notlower than 1.6650 angstrom.
 51. The conductive member of claim 47,wherein said intergranular phases are continuously formed.
 52. Theconductive member of claim 47, wherein said aluminum nitride ceramicscontains boron atoms in an amount of not lower than 1.0 weight percentand carbon atoms in an amount of not lower than 0.3 weight percent. 53.The conductive member of claim 47 containing a rare earth element in anamount of not smaller than 0.2 weight percent.